A critical need exists for a dosage form that makes available at a later time a drug to satisfy a therapeutic demand. The demand can arise during a circadian or chronological cycle, or the demand can arise for producing a therapeutic effect a later time, such as during the morning hours. For examples, many patients with myocardial infarction exhibit a clinical incidence of this syndrome that shows a circadian distribution with high frequency in the morning hours between 4:00 a.m. and 9:00 a.m., as reported in The American Journal of Cardiology, Vol. 62, pages 635 to 637, 1988; Circulation, Vol. 82, pages 897 to 902, 1990; and Heart Disease, Vol. 2, pages 1234 to 1235, 1988. Yet, the medical art, previously lacked a dosage form for administering a drug that provides therapy for this application during these critical hours.
There are dosage forms known to the prior art for delivering a drug continuously over time, such as disclosed in U.S. Pat. No. 4,327,725 issued to Cortese and Theeuwes, and in U.S. Pat. Nos. 4,612,008; 4,765,989; and 4,783,337 issued to Wong, Barclay, Deters and Theeuwes. The dosage forms disclosed in these patents comprise a semipermeable wall that surrounds a compartment. The compartment comprises a drug formulation, and in contact with the drug formulation, a displacement member that pushes the drug formulation from the dosage form. These dosage forms operate by imbibing fluid through the semipermeable wall into the compartment, wherein the fluid contacts and motivates the displacement member to consume space and thereby pushes the drug formulation from the dosage form. These dosage forms operate successfully for their intended use, and they can deliver many difficult to deliver drugs for their intended purpose. One limitation, however, associated with these dosage forms, consists in the dosage form immediate delivery of drug to a drug recipient. That is, the dosage forms do not provide for the delayed delivery of a drug to satisfy a future therapeutic need.
It is immediately apparent in the light of the above presentation that a pressing need exists for a dosage form that can delay the delivery of a drug to provide a drug-free interval and then deliver a dose of drug. It will be appreciated by those versed in the dispensing art, that if a novel and unique dosage form is made available for executing a therapeutic program comprising a drug-free interval followed by a drug-delivery interval, such a delayed drug-delivery dosage form would have a practical application, and it would also represent a valuable contribution to the medical arts.